1. Field of the Invention
The present invention relates to an information processing apparatus and an information processing method, and more particularly to an information processing apparatus and an information processing method for reducing the burden of a transcoding process for converting a format such as the compression ratio of a code stream, the resolution of an image, a color format, or the like.
2. Description of the Related Art
Archive systems or image databases that have heretofore been available store uncompressed images referred to as master images. For retrieving stored uncompressed images as needed, they are compressed into a compressed file that will be distributed through a network or saved in a recording medium.
In filmmaking, images are captured on 35-mm or 60-mm films and then converted into digital image data by an apparatus referred to as a film scan converter. The digital image data serve as master image data.
In the medical field, images captured on films are similarly converted into digital image data as master image data by a film scan converter, though some X-ray photographic image data may be directly used as uncompressed image data.
Many modern single-lens reflex digital cameras allow RAW data or RGB data acquired from a CCD (Charge-Coupled device) or a CMOS (Complementary Metal Oxide Semiconductor) image sensor to be saved as uncompressed image data in a memory card.
Although uncompressed master image data are important and desirable as they are free of lossy data, they tend to be large in data size. For transferring master image data through a network or recording large master image data in a memory card, they need to be compressed or encoded in some way.
For storing master image data in a hard disk, it has been customary to losslessly compress the master image data into a lossless compression file, and store the lossless compression file in the hard disk. In this case, it is convenient to save the master image data in an inexpensive recording medium such as a tape.
In the applications of digital cinema, a format for compressing master image data for distributing movies is determined according to DCI (Digital Cinema Initiatives). According to the DCI specifications, JPEG (Joint Photographic Experts Group) 2000 Part-1 as an ISO (International Organization for Standardization) standard is used as the compression and expansion technology, and the bit rate has a peak rate of 250 Mbps for a moving image sequence of XYZ 12 bits (24 Hz) at an image size of 4,096×2,160 pixels. Master image data need to be encoded at the above bit rate for distribution and projection.
The DCI specifications are addressed to the resolution of 4,096×2,160 pixels which is four times the resolution of HDTV (High Definition Television). According to the DCI specifications, therefore, it is often customary to losslessly compress master image data into a data size which is a fraction of the original data size and store the compressed image data in a storage medium such as a hard disk.
The image data stored in the storage medium are subsequently losslessly expanded into baseband data, which are then irreversibly compressed into a JPEG 2000 file according to the DCI standard by the JPEG 2000 lossy compression technique.
Codec techniques other than JPEG 2000 include MPEG-2 (Moving Picture Experts Group-2) for satellite digital broadcasts and H.264 Video Codec for one-segment broadcasts. Therefore, there are instances where image data compressed by JPEG 2000 need to be converted into formats according to other codec techniques such as MPEG-2 and H.264 Video Codec. While high-resolution image data such as digital cinema data are often processed by JPEG 2000, image data having resolutions lower than the HDTV resolution are mainly processed by MPEG-2 and H.264 Video Codec. Consequently, when image data are transcoded from the JPEG 2000 format into the MPEG-2 or H.264 Video Codec format, the resolution of the image data may also need to be converted at the same time.
For data conversion, there are known down decoders for performing an inverse discrete cosine transform using only coefficients of low-frequency components of DCT blocks of a bit stream of high-resolution image data to decode them into standard-resolution image data. For details, reference should be made to Japanese patent No. 4016166 and Japanese patent No. 4026238, for example.